Changes in Past, Present, and Future Sea Level on the Coast of Norway
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J. Even Ø. Nilsen, Helge Drange, Kristin Richter, Eystein Jansen and Atle Nesje : Changes in past, present, and future sea level on the coast of Norway a project by Nansen Environmental and Remote Sensing Center and UNI Research, at the Bjerknes Centre for Climate Research, funded by the City of Bergen, Department of Urban Development, Climate, and Environmental Aairs. NERSC Special Report no. 89 Bjerknes Centre for Climate Research publication no. R101 Bergen, August 2012 This is NERSC Special Report 89, publication no. R101 from the Bjerknes Centre for Climate Research. The main parts of this report are to be cited as follows. Chapter 4 is to be cited as: Jansen, E. (2012). Paleoclimatic perspectives on sea level. In Nilsen, J.E.Ø., H. Drange, K. Richter, E. Jansen, A. Nesje. Changes in the past, present, and future sea level on the coast of Norway. NERSC Special Report 89, Bergen, Norway. Chapter 5 is to be cited as: Richter, K., J.E.Ø. Nilsen, H. Drange (2012). Contributions to observed sea level change for1960-2010. In Nilsen, J.E.Ø. , H. Drange, K. Richter, E. Jansen, A. Nesje. Changes in the past, present, and future sea level on the coast of Norway. NERSC Special Report 89, Bergen, Norway. Chapter 6 is to be cited as: Drange, H., J.E.Ø. Nilsen, K. Richter, A. Nesje (2012). Updated estimates of future sea level rise on the Norwegian coast. In Nilsen, J.E.Ø., H. Drange, K. Richter, E. Jansen, A. Nesje. Changes in the past, present, and future sea level on the coast of Norway. NERSC Special Report 89, Bergen, Norway. The published article in Appendix 2 is to be cited as: Richter, K., J.E.Ø. Nilsen, H. Drange (2012). Contributions to sea level variability along the Norwegian coast for 1960-2010. J. Geophys. Res., 117, doi:10.1029/2009JC007826. The full report is to be cited as: Nilsen, J.E.Ø., H. Drange, K. Richter, E. Jansen, A. Nesje. (2012). Changes in the past, present, and future sea level on the coast of Norway. NERSC Special Report 89, Bergen, Norway. 48 pp. City of Bergen, Department of Urban Development, Climate, and Environmental Aairs: www.bergen.kommune.no/byutvikling Nansen Environmental and Remote Sensing Center: www.nersc.no Uni Research: www.uni.no Bjerknes Centre for Climate Research: www.bjerknes.uib.no University of Bergen: www.uib.no MARE: www.mare-project.eu August 2012 Changes in the past, present, and future sea level on the coast of Norway1 Project report to the City of Bergen, Department of Urban Development, Climate, and Environmental Affairs 1,2 3,2 4,2 5,4,2 5,2 Jan Even Øie Nilsen , Helge Drange , Kristin Richter , Eystein Jansen and Atle Nesje 1 Nansen Environmental and Remote Sensing Center, Bergen 2 Bjerknes Centre for Climate Research, Bergen 3 Geophysical Institute, University of Bergen 4 Uni Research AS, Bergen 5 Department of Earth Science, University of Bergen Sea levels are rising, predominantly due to the warming of the oceans, melting of land- based ice, and ground water depletion. In addition land surfaces rise and sink. The west coast of Norway is still rising after the retreat of the Fennoscandian ice sheet of the last ice. Presently, the rates of ocean and land rise are comparable, but under global warming the sea levels on the Norwegian coast are expected to rise by 20 to 80 cm by the end of the century. In 50 years about half of this rise is estimated. In the latter half of this century the expected sea level rise will impose increased challenges upon existing infrastructure, and adapting plans for new infrastructure to an ever-rising sea level can be advantageous. In this research project, changes in sea level in prehistoric times as well as during the latest 50 years are studied, the state of the present sea level is assessed, and updated estimates for sea level rise in the 21st century is presented. 1 To be cited as Nilsen, J.E.Ø., H. Drange, K. Richter, E. Jansen, A. Nesje (2012). Changes in the past, present, and future sea level on the coast of Norway. NERSC Special Report 89, Bergen, Norway. 48 pp. 1 August 2012 Table of Contents 1. Summary............................................................................................................................... 3 2. Administrative details...................................................................................................... 4 3. Introduction......................................................................................................................... 4 4. Paleoclimatic perspectives on sea level .................................................................... 5 Mean sea level ...................................................................................................................................... 5 Rates of change .................................................................................................................................... 6 5. Contributions to observed sea level change for 1960-2010................................ 8 Methods .................................................................................................................................................. 9 Results...................................................................................................................................................10 Discussion............................................................................................................................................12 Conclusions .........................................................................................................................................13 6. Updated estimates of future sea level rise on the Norwegian coast ...............14 Background .........................................................................................................................................14 Observed sea level rise....................................................................................................................15 Global sea level in the future.........................................................................................................15 Regional sea level in the future ....................................................................................................17 7. Dissemination ...................................................................................................................21 Bibliography ..............................................................................................................................22 Appendix.....................................................................................................................................24 Appendix 1: Estimates of future sea level rise for the Norwegian coastal municipalities.....................................................................................................................................24 Appendix 2: Peer review publication on sea level change during the past 50 years .31 2 August 2012 1. Summary The estimated global sea level rise for the two recent decades is 3 mm/yr, twice as fast as the average rise throughout the last century. We know the surface of the oceans will continue to rise for a long time into the future, even hundreds of years after humanity learns how to control greenhouse gas emissions. In this project, prehistoric sea level and rates of change have been assessed, the mechanisms involved in sea level rise have been studied based on observations from modern times, and future sea level rise has been estimated based on the current knowledge. About 3 million years ago, when the continents were already in today's positions, the climate on Earth was significantly warmer than today, the large ice sheets of Greenland and Antarctica were smaller and the sea level 10-30 m higher. During the last interglacial (about 120.000 years ago) global temperature was about 1-2°C warmer than today. The sea level was 4-10 m higher, mainly due to less water stored as ice on land and the thermal expansion of the oceans. The sea level change during the last interglacial was around 2 mm/yr, which is comparable to the presently observed rates. If today's ice sheets of Greenland and West-Antarctica were to become unstable and partly collapsing, sea level rates may become similar to those found after the ice ages. These rates have been estimated to be up to 40 mm/yr at certain locations. In modern times, the different processes affecting regional sea level change can be studied using various observations. In the study focussing on the Norwegian coast, it is shown that short-term changes in local sea level are to a large extent caused by changes in temperature (thermal expansion) and salt content (haline contraction) of seawater, as well as changes in local atmospheric pressure. In contrast, less than half of the observed long-term changes (the trend) can be explained by these processes and land uplift. In fact, apart from the land uplift, only thermal expansion contributes to a significant trend along the entire Norwegian coast. The observed trend in relative sea level (the sea level observed from shore) is 0.9 mm/yr in Bergen in the period 1960-2010. For the absolute sea level (i.e. without compensating for land uplift) the rise would be 2.6 mm/yr. Of this 0.9 mm/yr can be attributed to thermal expansion, and 0.7 mm/yr is estimated to be due to melting land ice. The remainder is subject to different processes with large uncertainties, and further research is necessary to accurately quantify their importance. Future sea level rise can be estimated by combining